Field of Invention
The invention relates to the field of integrated optics chips or devices and more particularly to the field of multifunction integrated optics chips such as those having integrated optic circuits formed on Lithium Niobiate (LiNbO.sub.3) substrates. Integrated optics chips are designed to include waveguides and to perform functions such as "Y", "Y--Y", or Star splitters, or couplers, polarizer, WDM (Wavelength Division Multiplexer) and modulators. Multiple functions are incorporated on a single device eliminating losses and errors associated with individual interface optical coupling.
The devices are fabricated in large numbers usually on three to four inch circular wafers of Lithium Niobiate (LiNbO.sub.3) using conventional photomasks, vacuum deposition, chemical baths and etching techniques to form large numbers of identical components at low cost and with high reliability. MIOC's (Multifunction Integrated Optics Chips or Circuits or Components) capable of performing many of the aforementioned functions are necessary for the fabrication of middle and high accuracy FOG's (fiber optic gyros) or rotation sensors that rely on the principle of Sagnac interferometers and possibly other interferometric fiber optic sensors such as hydrophones that rely on the principles of the Mach-Zehnder or Michaelson Interferometers requiring high stability.
While performing ramped temperature environmental tests, FOG Instruments, that were exhibiting excessive power hysteresis, exhibited improved power hysteresis performance when the input modulation test rails or plates that were positioned on the surface of the MIOC to straddle the input waveguide were shorted together. Test rails or plates had been formed for use as a birefringence modulator, on MIOC devices, to facilitate testing for PNR (polarization non-reciprocity) when devices were operated in a FOG instrument. The test required that the rails function as modulator plates along the input waveguide. The plates were therefore isolated from each other so that they could be driven by a switching waveform in the course of the PNR test.
The device was made of Lithium Niobiate (LiNbO.sub.3) and was similar in size to the dimensioned related art device shown in FIG. 1.
The hysteresis problem exhibits itself as a slight change in the power of a device as the device is first taken through a positive or negative temperature change followed by a negative or positive temperature change. The charge differential that develops across the face of the chip results in a charge leakage across the face of the chip. The time and temperature dependent effects combine to contribute to hysteresis in the transmitted power of the device and to the efficiency of the waveguides in the device to propagate light.
As further background, Integrated optics chips, such as those characterized in this application are formed using processes and steps similar to some of those found in related U.S. Patents such as U.S. Pat. No. 5,037,205 filed Sep. 25, 1989 for a "INTEGRATED OPTIC INTERFEROMETRIC FIBER GYROSCOPE MODULE AND METHOD" which issued to George A. Pavlath on Aug. 6, 1991 which shows a birefringence modulator comprising two electrodes formed on opposite sides of the waveguide; U.S. Pat. No. 5,193,136 filed Nov. 26, 1991 for a "PROCESS FOR MAKING MULTIFUNCTION INTEGRATED OPTICS CHIPS HAVING HIGH ELECTRO-OPTIC COEFFICIENTS" which issued to Dr. Chin L. Chang et al on Mar. 9, 1993; U.S. Pat. No. 5,046,808 filed Dec. 18, 1989 for an "INTEGRATED OPTICS CHIP AND METHOD OF CONNECTING OPTICAL FIBER THERETO" which issued to Dr. Chin L. Chang On Sep. 10, 1991; U.S. Pat. No. 5,393,371 filed Jun. 21, 1993; for a "INTEGRATED OPTICS CHIPS AND LASER ABLATION METHODS FOR ATTACHMENT OF OPTICAL FIBERS THERETO FOR LiNbO.sub.3 SUBSTRATES" which issued to Dr. Chin L. Chang et al on Feb. 28, 1995; U.S. Pat. No. 5,442,719 for an "ELECTRO-OPTIC WAVEGUIDES AND PHASE MODULATORS AND METHODS FOR MAKING THEM" which issued to Dr. Chin L. Chang et al on Aug. 15, 1995.
U.S. Pat. No. 4,976,506, filed Feb. 13, 1989 for "METHODS FOR RUGGED ATTACHMENT OF FIBERS TO INTEGRATED OPTICS CHIPS AND PRODUCT THERE OF" which issued to Dr. G. Pavlath on Dec. 11, 1990 and U.S. Pat. No. 5,146,522, filed Jun. 18, 1991 for "METHODS FOR RUGGED ATTACHMENT OF FIBERS TO INTEGRATED OPTICS CHIPS AND PRODUCT THERE OF" which issued to Dr. G. Pavlath on Sep. 8, 1992 teach known methods for attaching pigtail fibers such as fiber 39, 29, 35 to respective optical ports 20, 28 and 34. The "522" patent teaches a "first plate attached to a first surface of the chip". Each of the foregoing patents have a common assignee, Litton Systems Inc. of Woodland Hills, Calif. Each of the foregoing patents cited herein are incorporated herein by reference for the purpose of providing those skilled in the art with background information on how integrated optics chips or multifunction integrated optics circuits are made.
In addition to the above patents, an early paper was titled "Short-and Long-term Stability In Proton Exchanged Lithium Niobiate Waveguides" by Janet Lehr Jackel and Catherine E. Rice of AT&T Bell Laboratories, Holmdel, N.J., 07733 appeared in SPIE Vol 460, Processing of Guided Wave Optoelectronic Materials (1984) at page 43 is of interest.
This application is particularly directed to methods and apparatus for the reduction of errors produced in an integrated optics chip formed to function as an optical modulator as a result of temperature differences across the surface of chip due to the Pyroelectric Effect or due to rapid changes in the temperature of the chip. A second application having U.S. Ser. No. 09/123,955, to formalize provisional application Ser. No. 60/080,260, filed Mar. 31, 1998 for a "Low Cost High Reliability Method of Correcting Pyroelectric Errors In Integrated Optics Chips" by Ken Shafer et al (now U.S. Pat. No. 5,044,184). Ser. No. 09/123,955 issued into U.S. Pat. No. 6,044,184 on Mar. 28, 2000 having a common assignee is incorporated herein by reference in its entirety.